The present invention relates to a display apparatus using as its display elements light-emitting elements typified by light-emitting diodes (LEDs) and organic EL (Electro Luminescence) elements.
JP-A-10-223373 discloses a display in which the cathode electrode patterns are formed such that the odd-numbered ones lead to one side of the substrate and the even-numbered ones lead to the opposite side in order to provide a uniform luminance distribution over the entire screen.
JP-A-2000-194428 discloses a device for driving organic EL elements, which employs a plurality of current sources (for example, 5 current sources) for each organic EL element and can change the current flowing in each organic EL element through selection control of the current sources so as to prevent occurrence of uneven luminance distribution due to variations among the current sources and among the forward voltages of the organic EL elements. The above JP-A-2000-194428 also discloses a technique for adjusting the luminance of each organic EL element by adjusting its light emission time period.
JP-A-2000-187467 discloses a technique for detecting the current flowing through each organic EL element by use of a current detecting circuit and controlling the next light emission time period of the element based on the detected current value, making it possible to detect and correct luminance variations among the elements due to variations among the original characteristics of the elements or degradation of the elements and thereby provide favorable gray scale control.
U.S. Pat. No. 6,291,942 (JP-A-2001-13903) discloses a technique for detecting the degradation degree of each light-emitting element based on the value of its current or luminance or a time characteristic to generate degradation information, and adjusting the time period during which a constant voltage is applied to the light-emitting element or no constant voltage is applied based on the generated degradation information.
The invention described in the above JP-A-10-223373 is disadvantageous in that high-luminance and low-luminance lines are alternately produced near each edge of the screen, and therefore an uneven luminance distribution may occur. Furthermore, since the current flowing through each light-emitting element varies according to its luminance, the amount of supply current changes depending on the number of pixels actually emitting light. That is, the amount of reduction in the luminance of each pixel due to the supplied current depends on the display data. The above JP-A-10-223373 takes into account that a voltage drop occurs between a light-emitting dot near the lead-out portion of the electrode pattern and that far from the portion. However, it gives no consideration to the fact that the amount of reduction in the luminance of each pixel due to the supplied current varies depending on the display data.
The invention described in the above JP-A-2000-194428 prevents occurrence of uneven luminance distribution due to variations among the current sources and among the forward voltages of the organic EL elements. However, this patent application gives no consideration to how to reduce the decrease in the luminance of each display element due to the voltage drop across the wiring from the current source to the display element or reduce occurrence of uneven luminance distribution due to luminance reduction variations among the display elements.
The above JP-A-2000-194428, JP-A-2000-187467, and U.S. Pat. No. 6,291,942 (JP-A-2001-13903) only correct luminance variations among the display elements due to variations among the original characteristics of the elements or degradation (secular change) of the elements. They give no consideration to how to reduce the decrease in the luminance of each display element due to the voltage drop across the wiring from the current source to the display element or reduce occurrence of uneven luminance distribution due to luminance reduction variations among the display elements.